It’s a great time to check out the latest .NET 9 Preview! We just shipped our sixth preview release, adding to some great features in the previous previews with major enhancements across the .NET Runtime, SDK, libraries, C#, and frameworks including ASP.NET Core, Blazor, and .NET MAUI. Check out the full release notes linked below and get started today.

This release contains the following improvements:

📚Libraries:

• Improvements to System.Numerics
• Support Primary Constructors in Logging Source Generator
• System.Text.Json enhancements including a new JsonSchemaExporter, nullable annotations recognition, requiring non-optional constructor parameters, ordering JsonObject properties, and new contract metadata APIs
• [GeneratedRegex] can now be used on properties
• New EnumerateSplits method for Regex to split more collection types
• Introduction of generic OrderedDictionary with OrderedDictionary<TKey, TValue>
• New ReadOnlySet<T> when needing to create a read-only wrapper around ISet<T>
• allows ref struct used in many places throughout the libraries
• Collection lookups with spans
• More span-based APIs including StartsWith and EndsWith extension methods
• Base64Url for optimized encoding and decoding
• SocketsHttpHandler by default in HttpClientFactory
• TLS resume with client certificates on Linux
• New System.Net.ServerSentEvents library providing a parser for easily ingesting server-sent events
• Introducing the Metrics Gauge Instrument in System.Diagnostics.Metrics to record non-additive values when changes occur
• Full release notes

⏱️Runtime:

• ARM64 Code Generation now adds ability to store operations
• Code Layout – RyuJIT’s block reordering algorithm with a simpler, more global approach
• Loop Optimizations for code size reduction and performance improvements
• Reduced Address Exposure through RyuJIT improvements to better track usage of local variable address
• AVX10v1 Support, a new SIMD instruction set from Intel
• Hardware Intrinsic Code Generation
• Constant Folding for Floating Point and SIMD Operations
• Full release notes

🛠️SDK

• NuGetAudit now raises warnings for vulnerabilities in transitive dependencies
• Addition of dotnet nuget why to find out why a transitive package is being used in your project
• MSBuild BuildChecks to help users enforce rules and invariants during their builds
• Full release notes

You can find detailed release notes for additional features in .NET 9 Preview 6 below:

C#

• Partial properties
• Full release notes

🌐ASP.NET Core

• Fingerprinting of static web assets ensuring that stale assets aren’t used and enables improved caching behavior for faster load time
• Improved distributed tracing for SignalR with a new ActivitySource
• Enhancements to Microsoft.AspNetCore.OpenAPI including completion enhancements, support for [Required] and [DefaultValue] attributes, schema transforms on OpenAPI documents,
• Analyzer to warn when [Authorize] is overridden by [AllowAnonymous], and new analyzers,
• ComponentPlatform renamed to RendererInfo
• Split large HTTP/2 headers across frames
• Full release notes

📱.NET MAUI

• Full release notes

🚀Get started

To get started with .NET 9, install the .NET 9 SDK.

If you’re on Windows using Visual Studio, we recommend installing the latest Visual Studio 2022 preview, or get started with Visual Studio Code and the C# Dev Kit extension.

📢Team Announcements & Discussions

The team has been making monthly announcements alongside full release notes on the dotnet/core GitHub Discussions and has seen great engagement and feedback from the community. We will continue to post each new release on GitHub, but as we get closer to launch this November alongside .NET Conf 2024 (save the date today!), we wanted to cross-post our release details on the .NET blog.

Discuss this release with the product teams on GitHub through the GitHub discussion announcement for this release.

• .NET 9 Preview 6 Discussion
• .NET Libraries & Runtime Discussion
• .NET MAUI Discussion
• ASP.NET Core Discussion

🔔Stay up to date with .NET 9

You can stay up-to-date with all the features of .NET 9 with:

• What’s new in .NET 9
• What’s new in C# 13
• What’s new in ASP.NET Core
• What’s new in .NET MAUI
• What’s new in EF Core
• Breaking Changes in .NET 9
• .NET 9 Releases

Additionally, be sure to subscribe to the GitHub Discussions RSS news feed for all release announcements.

We want your feedback, so head over to the .NET 9 Preview 6 GitHub Discussion to discuss features and give feedback for this release.